A multitude of different communication terminals and devices have been developed for packet-based multimedia communication using IP (Internet Protocol), such as fixed or mobile computers and telephones. Multimedia services typically involve transmission of media in different formats and combinations. For example, a user terminal may exchange audio information as well as visual information with another user terminal, or may download or stream media in any format from a content server. Further, two user terminals may share multimedia content downloaded or streamed from a server, and so forth.
An architecture called “IP Multimedia Subsystem” (IMS) has been developed as a platform for enabling multimedia services and sessions, commonly referred to as an IMS network or IMS core. Thus, an IMS network can be used to initiate and control multimedia sessions for user terminals connected to different access networks. Although conceived primarily to enable multimedia services for mobile IP terminals, the IMS concept can be used by fixed IP terminals as well.
Multimedia sessions are handled by specific session control nodes in the IMS network including the node called P-CSCF (Proxy Call Session Control Function) acting as the entry point towards the IMS network for user terminals. An IMS network also includes a database node HSS (Home Subscriber Server) for storing various subscriber and authentication data, and may further include application servers for enabling various multimedia services.
The signalling protocol called “SIP” (Session Initiation Protocol) is commonly used for signalling various messages during setup of multimedia sessions in IMS networks. For example, a terminal typically sends a message called “SIP INVITE” to initiate a session with another terminal or a server, e.g. when a multimedia application has been invoked in the terminal. The SIP INVITE message triggers different actions in the IMS network and the access network for establishing the session, including reservation of appropriate network resources, which will be described in more detail later below.
In SIP, an additional protocol called “SDP” (Session Description Protocol) is used for specifying various parameters of a multimedia session, and an SDP message is typically embedded as a self-contained body within SIP messages. SDP messages are used to provide information on terminal capabilities and media properties, in order to specify and negotiate session parameters for multimedia sessions, which is well-known in the art. The term “session parameters” is used here to represent any terminal capabilities, media properties and address information necessary to establish a session. The above-mentioned SIP INVITE message and a common response message “SIP 200 OK” typically include an embedded SDP message with information on, e.g., one or more codecs (coders/decoders) proposed by the sender for the session.
A policy node associated with the used access network is also connected to the IMS network. The policy node is basically responsible for authorising sessions for terminals connected to the associated access network, and for controlling the network resource reservation for the sessions, based on various predetermined policies and subscription profiles. According to current terminology, the policy node generally operates according to a function called PCRF (Policy and Charging Rule Function). In particular, different QoS (Quality of Service) requirements can be controlled by the policy node for different services and/or subscribers which will determine the above resource reservation.
Many communication services thus require a certain QoS in order to provide a satisfying and expected result to subscribers. When establishing a communication session for a subscriber, various network resources are reserved for the session to provide a bearer of media data, preferably such that an acceptable and expected level of service is maintained for the subscriber, e.g. with respect to data bitrates and latency.
Today, differentiated services and subscriptions are commonly offered to subscribers such that they can consume services with different subscription types that typically dictate the QoS requirements for those services. Thus, subscribers may be offered specific service levels with respect to QoS for different subscription types and also for individual services. For example, using current terminology, a “Platinum” subscription may provide a relatively high warranted quality or service level, whereas “Gold”, “Silver” and “Bronze” subscriptions provide successively lower service levels.
Moreover, specific services may also be offered with different service levels, e.g. at different prices. This differentiation of subscriptions, services and quality/service levels becomes increasingly significant and will thus influence the customer satisfaction and expectations to a great extent. For example, a Bronze subscriber might be satisfied to obtain a certain service level whereas a Platinum subscriber might not, expecting a higher service level.
When reserving network resources during setup of an IMS-controlled session, the above aspects of quality requirements must be considered, which is illustrated by the following example. In FIG. 1, a conventional session setup procedure is shown where a terminal A will communicate multimedia with another terminal B, e.g. using a wireless connection although the figure is generally also valid for fixed connections. Terminal A is connected to an access network in which a gateway node GW 100, e.g. GGSN (Gateway GPRS Switching Node) in a wireless access network, is used for data transport in the “bearer plane”. Among other things, the IMS network includes a P-CSCF node 102 used for SIP-based control signalling with terminal A in the “control plane”, and an AF (Application Function) 104 enabling the service used. In this example, terminal B is connected to another access network, not shown.
The gateway node GW 100 is connected to an associated policy node 106, here denoted PCRF, which is thus responsible for authorising communication sessions. The policy node 106 also controls resource reservation in the associated access network, as mentioned above, based on information stored in an SPR (Subscription Profile Repository) and a policy database, which are not shown here.
In a first step 1:1, terminal A obtains an initial connection and data bearer with the access network as established by the gateway node GW 100, e.g. involving the activation of a primary PDP context and a Radio Access Bearer RAB in the wireless connection case. The established connection and bearer are primarily used for carrying occasional control messages such as service requests, allowing for relatively low bandwidth and fairly long delays.
In a next step 1:2, GW 100 sends relevant access information to PCRF 106, including a subscription identifier and information on the connection and data bearer established in step 1:1. Thereby, a “state” is created in PCRF 106 for a “bearer session”, meaning that the received access information is retained for terminal A in PCRF 106. A certain basic service level, typically a “best effort” level, has now also been established basically for communication of control messages using the obtained data bearer.
When a user activates a selected application in terminal A in order to communicate with terminal B in this case, a session negotiation is performed in a following step 1:3, which may involve the exchange of terminal capabilities with terminal B using the above SDP message. Terminal A starts the session negotiation by sending a SIP INVITE message towards terminal B, containing an SDP message with session parameters such as one or more proposed codecs for the session, referred to as an “SDP offer”. Terminal B then responds with another SDP message, referred to as an “SDP answer”, and the negotiation goes on until session parameters have been settled that both terminals are prepared to use.
After the session negotiation, the P-CSCF node 102 sends corresponding service information to PCRF 106, in a next step 1:4. Thereby, another state is created in PCRF 106 for a “service session”, meaning that the received service information is retained. Moreover, PCRF 106 determines whether the requested session can be allowed or not by applying a suitable policy. In particular, it is checked which service level terminal A is entitled to during the forthcoming session, which may depend on the subscription type and/or service offerings from the network operator, both of which may be service-specific in different ways, e.g., depending on the time of day, week or season, and so forth.
If PCRF 106 can allow the requested session, i.e. according to the applied policy for the given subscriber and service and using the negotiated session parameters, an OK message is sent to the P-CSCF node 102 which also sends an OK message to the terminal A, as illustrated in a step 1:5. In order to satisfy QoS requirements according to the subscription and/or service offerings, appropriate network resources should now be reserved for the session, such as establishing a new data bearer. In this example, terminal A issues a bearer request for service data transport to GW 100, in a next step 1:6. Alternatively, the establishment of bearer may be initiated by the access network.
In a further step 1:7, GW 100 reserves network resources by establishing a suitable new bearer for the forthcoming data transport, e.g. involving the activation of a secondary PDP context and a new Radio Access Bearer RAB in the case of a wireless connection. GW 100 also sends relevant QoS information on the established connection and data bearer to PCRF 106 where the bearer session state is updated accordingly.
Hence, a service level with a certain QoS has now been established for the requested service, according to the negotiated session parameters and applied policy for the given subscriber and service. Likewise, network resources are established for terminal B as well, to create a service session and bearer of media data in the access network used by terminal B, based on a service level which terminal B is entitled to, which may be different from what terminal A has obtained.
Finally, after the individual service sessions of both terminals have been interconnected by the PCRF 106 in a binding operation, terminals A and B can execute the session, as illustrated by a final step 1:8. However, the data bearer established for terminal B by the opposite access network may provide a different service level depending on the subscription and/or service offerings of terminal B. In that case, data communicated between the two terminals A and B will be subject to different data bearers depending on the transport direction, where data sent from terminal A uses the bearer established for A and data sent from terminal B uses the bearer established for B. It should be noted that the above description of a conventional session setup procedure is greatly simplified by omitting details not necessary for understanding the present invention.
As mentioned above, subscribers consuming a communication service are often entitled to and may generally expect different service levels depending on their subscriptions and/or selected services. However, in order to achieve a certain service level and QoS in a multimedia session, the entire end-to-end path of media transport must share that service level. As can be seen from the example above, network resources are established in the respective access networks which may provide data bearers with different capacities for two communicating parties, if differentiated service levels are employed. In that case, it is known that a “least common denominator” with respect to data rates and codecs can be negotiated between two terminals A and B, by utilising the above-described SIP-embedded SDP offer/answer model as follows.
An SDP offer in a SIP INVITE message from terminal A can carry preconditions requiring that certain end-to-end characteristics are fulfilled before the media path can be established successfully. This SDP offer may be configured with optional session attributes “a” as follows:
SDP (SIP INVITE from A):
m=audio 20002 RTP/AVP 0
c=IN IP4 192.0.2.1
a=curr:qos e2e none
a=des:qos mandatory e2e sendrecv
This SDP offer specifies a proposed audio codec “m”, an IP address “c”, and two session attributes “a” with network resource parameters, the first one indicating that no end-to-end QoS resources are currently reserved, and the second one indicating that a certain desired end-to-end QoS is required (“mandatory”) in both path directions (“sendrecv”).
Network resources are then reserved for the receiving terminal B in its send direction, i.e. from B to A, and terminal B sends a response SIP 200 OK containing an SDP answer that may be configured as follows:
SDP (SIP 200 OK from B):
m=audio 30000 RTP/AVP 0
c=IN IP4 192.0.2.4
a=curr:qos e2e none
a=des:qos mandatory e2e sendrecv
a=conf:qos e2e recv
In this SDP answer, a third session attribute “a” has been added confirming that network resources have been reserved in a direction from B to A (“recv”), providing a certain end-to-end QoS that terminal B is entitled to obtain. Terminal B then waits for another SDP offer from A with a confirmation of reserved network resources in the opposite direction from A to B. This SDP negotiation continues until required network resources have been reserved for both directions.
However, terminal A will then receive data during the session over a data bearer providing a QoS to which terminal B is entitled, and vice versa. For example, if terminal A uses a platinum subscription and terminal B uses a bronze subscription, terminal A will receive data over B's data bearer which provides a service level that is lower than the expected service level according to the platinum subscription.
It is therefore a problem that a premium subscriber, entitled to and expecting a relatively high service level, may experience a service level that is lower than expected when communicating with a non-premium subscriber, due to the above differentiation of services and/or subscribers. The premium subscriber will thus not be able to utilise the service with a corresponding premium quality.